Pointing devices for entering commands into a computer are well known in the art, and include mice, joysticks, X-Y tablets, wire pens and trackballs. Trackball-type pointing devices include a housing supporting a rotatable ball and one or more depressible buttons. Electronic encoders sense rotation of the ball and generate a signal indicative of the ball's rotation to control movement of a cursor on a display screen of the computer. The ball protrudes from the top of the housing. The housing is usually positioned on a table top. The rotatable ball is exposed for rotation by the hand of a user. The housing may include one or more depressible buttons to enter commands into the computer, based on the position of the cursor on the display screen. Depressing the button permits the user to enter various commands into the computer, based on the location of the cursor. Examples of such commands include: depressing the button to pull down a menu; create starting, ending or other points in a graphic pattern on the screen; moving objects to different locations on the screen; and the like.
Many prior art trackball-type pointing devices are not easily usable-with laptop or portable computers. The trackball-type pointing device requires a work surface upon which the housing containing the ball must rest. Many times, a laptop or portable computer is used in an environment where an adequately sized table top or a table top itself is not provided. For example, laptop or portable computers may be used on an airplane tray table, or while resting in a user's lap. In each of these examples, no surface is readily available to a user upon which to place a trackball-type pointing device.
U.S. Pat. No. 5,187,468 describes a trackball-type pointing device attachable to a keyboard using an adjustable clamp. This pointing device permits its use in environments that lack a suitable work surface.
However, even users of larger sized computers and other systems where an appropriate work surface is available find it desirable to use this type of trackball-type pointing device.
In U.S. Pat. No. 5,187,468, a tilting mechanism allows the pointing device to tilt about an axis parallel to an edge of the keyboard. Using the tilting mechanism to tilt the device causes the device to swing through an arc. As a result, the elevational position of the ball and the housing supporting it changes significantly as the device is tilted. Further, the prior art pointing device projects a significant distance to the side of the keyboard to which it is attached and positions the ball far from the keyboard. Because of this movement and the size and location of the ball, more free space is needed in the area adjacent to the keyboard than is sometimes available.
Additional disadvantages of prior trackball-type pointing devices include their use of a large number of components to provide all of the above functions, particularly, attachment to a keyboard and the ability to be tilted.
Therefore, to overcome the above problems, there is a need for an improved pointing device removably attachable to a keyboard or computer that is capable of pivoting about an axis of rotation closer to the keyboard or computer to which it is attached. The pointing device should have a more compact, space-saving design. Also, since fewer components generally result in decreased manufacturing costs, there is a need for a pointing device removably attachable to a keyboard or computer that is capable of tilting which uses fewer components.